Values of the second thermodynamic dissociation constant pK(2) of N-[tris(hydroxymethyl)methyl-3-amino]propanesulfonic acid (Taps) have been determined at twelve temperatures from 278.15 K to 328.15 K including 310.15 K by measurements of the electromotive-force for cells without liquid junction of the type: Pt\H-2 (g, p(o) = 101.325 kPa)\Taps (m(1)), NaTapsate (m(2)), NaCl (m(3))\AgCl]Ag, where in denotes molality. The pK(2) values for the dissociation of Taps are represented by the equation: pK(2) = 2969.61 . (K/T) - 17.05052 + 2.73697 . ln(T/K). The values of pK(2) for Taps were found to be (8.502 +/- 0.0007) at T = 298.15 K and (8.225 +/- 0.0009) at T = 310.15 K, respectively, indicating thereby to be useful as buffer solutions for pH control in the region 7.4 to 8.5. The thermodynamic quantities, Delta G(o), Delta H-o, Delta S-o, and Delta C-p(o) dissociation process of Taps have been derived from the temperature coefficients of the pK(2). (C) 2005 Elsevier Ltd. All rights reserved.